350 is the red line for human beings, the most important number on the planet. The most recent science tells us that unless we can reduce the amount of carbon dioxide in the atmosphere to 350 parts per million, we will cause huge and irreversible damage to the earth.

In this exclusive lecture for Sydney Ideas leading environmental writer and activist Bill McKibben talks about how climate science and climate politics are quickly evolving–and how we now have a much more specific idea both of the peril we face and the steps (large and difficult) necessary to solve it.

Even two years ago, scientists could offer only vague ideas of how much carbon in the atmosphere was too much. But in the wake of the rapid melt of Arctic sea ice in 2007, it's become clear that this is a problem not for the future but very much for the present.

In addition, McKibben describes the swelling grassroots global movement, 350.org, which looks set to coordinate the largest day of global environmental action ever, with actions from high in the Himalayas to underwater on the Great Barrier Reef.

Bill McKibben

Environmentalist Bill McKibben is a scholar in environmental studies at Middlebury College.

McKibben is an American environmentalist and writer who frequently writes about global warming, alternative energy, and the risks associated with human genetic engineering. Beginning in the summer of 2006, he led the organization of the largest demonstrations against global warming in American history. McKibben is active in the Methodist Church, and his writing sometimes has a spiritual bent.

He is the author of The End of Nature (1989), the first book for a general audience about global warming. Recent books include Enough (2004), which critiques human genetic engineering and other rapidly advancing technologies; Wandering Home (2005), which catalogs his foot-travels across the Vermont landscape; and Age of Missing Information (2006), in which he compares his experience watching 1700 hours of videotaped TV to that of contemplating nature in the Adirondacks.

Deep Economy author Bill McKibben, co-founder and director of 350.org, emphasizes the immediate need for environmental reform, as well as the consequences of climate change that may already be beyond repair.

Deep Economy author Bill McKibben, co-founder and director of 350.org, presents the current concentration of carbon in the atmosphere, which has surpassed the redline of 350 ppm identified by scientists as the safe upper limit for C02 in the atmosphere.

Bill McKibben, co-founder and director of 350.org, talks about the sociological implications of fossil fuel dependence, including the weakening of societal bonds and a general decline in individual happiness.

McKibben foresees a return to localized economies as society is weaned from cheap fossil fuels.